The technology of wavelength division multiplexing (WDM) has been successfully utilized in optical networking in providing high-capacity data transmissions over a single fiber carrying multiple Gb/s wavelength channels.
In the evolution of optical networking, two types of nodes are generally considered: end nodes and network nodes. A WDM point-to-point link involving two end nodes 100 is illustrated by FIG. 1 where bi-directional transmission of 2N wavelength multiplexed channels are achieved using a single or a pair of optical fibers 110. Various types of devices function as the transmitters 101, receivers 102, and multi/demultiplexers 103. Typically, the transmitters 101 and receivers 102 are high-speed optoelectronic devices while the multi/demultiplexers 103 can be fiber-optic or intergrated-optic devices. An example of recently built WDM end node is the IBM model 9729 equipment with 20 wavelengths supporting up to 1 Gb/s per-channel bit rate over a &lt;75 km link; see U.S. Pat. No. 5,487,120, issued Jan. 23, 1996, by Choy et al., "Optical Wavelength Division Multiplexer for High Speed, Protocol-independent Serial Data Sources," which is hereby incorporated by reference in its entirety. Another example is the AT&T next generation lightwave network (NGLN) system with 8 wavelengths supporting SONET OC-48 signals (see C. Fan et al. "Planning the Next Generation Lightwave Network (NGLN) for Capacity Upgrade and Service Growth," presented at the European Institute R&D in Telecom, WDM Workshop Operators and Suppliers, Brussels, Aug. 14, 1995). Other examples include the Ciena 16-wavelength MultiWave Terminal and the Pirelli 32-wavelength WaveMux 3200 product, both supporting OC-48 channels (presented at the SuperComm '96, Dallas, Tex.).
An optical network in the form of a ring is illustrated by FIG. 2 where, in addition to the originating (add) and termination (drop) of traffic as in link end nodes, the ring nodes 202 also perform the function of wavelength routing. It is therefore commonly referred to as an optical add-drop multiplexer (OADM). A self-healing WDM ring network test-bed has been demonstrated by NTT (H. Toba, et al., "An Optical FDM-based Self-healing Ring Network Employing Arrayed Waveguide Grating Filters and EDFA's with Level Equalizers," IEEE Journal of Selected Areas in Communications, vol. 14, pp. 801-813, June 1996) in which up to 15 wavelengths enter the network at the central node while channels of specified wavelength are dropped and added in each remote node. Another OADM recently demonstrated is the Alcatel Telecom MADO prototype (presented at the SuperComm '96, Dallas, Tex.) for 4 wavelengths supporting OC-48 signals. For dynamic wavelength routing, optical space switches 201 are normally required as shown in FIG. 2.
Thus, there is a need for a system and method for modularly upgrading an N-wavelength WDM point-to-point link end node to either a 2N wavelength WDM point-to-point link end node or to a ring node having the required add-drop capabilities. The present invention addresses such a need.